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Effects of ZrO2 on thermal stability and crystallisation of K2O–Al2O3–SiO2 glasses

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The thermal stability and crystallization behaviour of two refractory glass-forming compositions in the K2O–Al2O3–SiO2 ternary system were studied without ZrO2 additions (samples KAS1 and KAS2, with compositions on the tie-lines from KAlSiO4 to Al2O3 and from KAlSi2O6 to Al2O3, respectively) and with ZrO2 additions (samples KAS1-Z and KAS2-Z). X-ray diffraction (XRD) was used to determine the crystalline phases formed during the heat treatment of the glasses. All as-prepared glasses were amorphous, except KAS2, with a weak SiO2 phase attributed to imperfect melting of starting materials, which disappeared upon heat treatment. Full crystallisation of kalsilite (KAlSiO4) was observed in sample KAS1 after only 5 min heat treatment at 1250°C; for sample KAS2, a minor phase transformation from γ-Al2O3 to α-Al2O3 was observed after 10 min heat treatment at 1250°C; the relict SiO2 phase disappeared and the major phase leucite (KAlSi2O6) began to form after 30 min in sample KAS2. Upon addition of ZrO2 (sample KAS2-Z) the transformation from γ-Al2O3 to α-Al2O3 was delayed and observed after 30 minutes' heat treatment at 1250°C. Meanwhile, the promotion of kalsilite and leucite crystallisation was observed in samples KAS1-Z and KAS2-Z, respectively. Differential scanning calorimetry (DSC) was used to determine characteristic temperatures and crystallisation activation energies (Ea) for each glass. However, there was no clear correlation between crystallisation tendency (glass-forming ability) and Ea for these glasses, which exhibit high crystallisation tendency. Multiple glass stability parameters (Hrubý KH, Weinberg KW, Lu & Liu KLL) were calculated based on characteristic temperatures and a further criterion (Hu k) was calculated, based on Ea. Promotion of the major phase (kalsilite and leucite) crystallization by the addition of ZrO2 was confirmed through these criteria.

Document Type: Research Article

Publication date: October 1, 2021

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